This invention relates to the barrel of a zoom lens employing a reflection-type optical system and having an aperture scale.
A zoom lens employing a reflection-type optical system has not yet been commercially produced; however, the same is the subject of U.S. Pat. No. 4,445,756 to the instant applicant.
Heretofore, a lens employing a reflection-type optical system has been mainly realized as a supertelephoto lens because it has less chromatic aberration and is considerably compact. However, it is disadvantageous in that, since the second mirror at the center of the lens blocks light, it is impossible to provide aperture means for the lens. Accordingly, with such a lens, the quantity of light is adjusted by the use of an ND filter. In order to replace the ND filter, threads are formed in the rear portion of the lens, or a filter insertion mechanism is provided. Alternatively, the lens may incorporate a turret type filter assembly. However, these methods are disadvantageous in that replacement is troublesome, the internal construction of the device is intricate, and the filter cannot be built into a small, light lens.